This application claims priority under 35 U.S.C. xc2xa7xc2xa7119 and/or 365 to 9804509-9 filed in Sweden on Dec. 22, 1998; the entire content of which is hereby incorporated by reference.
The present invention is directed to a connection of a terminal of a high frequency (HF) component and a terminal of an adjacent substrate, whereby the high frequency component and the substrate are being mounted on a common carrier. Moreover, the invention is directed to a process for accomplishing such a connection and a hybrid circuit having such a connection.
More specifically, the invention concerns a wire bond connection between an electrical terminal of a monolithic integrated circuit (MIC); especially a microwave monolithic integrated circuit (MMIC), and a terminal of the substrate. The substrate terminals could serve so as to connect the terminals of the MIC to electrical components or circuits mounted on the substrate or other peripheral devices.
In order to avoid signal losses and high frequency signal deterioration and in order to ensure good mechanical stability of wire bonding connections used in connection with monolithic integrated circuits, it is of high importance to keep the length of the bond wires as small as possible.
However, current production methods are associated with relatively wide tolerances for the distance between the MIC and the substrate. In order to accomplish a certain success rate using current mass production methods, this distance is chosen to include a certain safety margin.
Consequently, the functionality of the high frequency circuitry of demanding applications may be adversely affected or special measures will have to be implemented in the actual electrical circuit so as to compensate for the adverse electrical characteristics induced. This again, is likely to increase the cost of the product.
In prior art document EP-A-0 803 907 the problems of unwanted inductances or discontinuities of impedances appearing in bonding wires, or circuit parts associated with bonding wires, have been dealt with.
According to the above document various solutions have been proposed, which focus on providing a range of prefabricated bonding elements with various characteristics. From this range of bonding elements, denoted ribbons, an appropriate bonding element having a certain predetermined inductance or impedance that match the given application is selected.
The bonding elements according to the above document are formed like ribbons having various protrusions, width variations or curvature, which result in varying impedance values.
It is understood that the above bonding elements do not provide for a limitation of the production tolerances involved, but seeks to provide a remedy for alleviating or obviating the adverse electrical effects which would have been induced had bonding wires of a standard configuration been used.
The fact that a variety of different elements must be handled during the mounting process according to EP-A-0 803 907, implies that it is complicated and expensive to automate this process. It should be noted that the desired precision by which the impedance value of the connection can be achieved, i.e. the desired resolution in impedance values, would depend on the actual number of different bonding elements, which can be provided.
A general problem with ribbons is that in order to achieve an acceptable impedance value (capacity value per length unit) it is typically required that the width of the ribbon must exceed the width of the substrate terminal. This involves some design constraints.
A further disadvantage is that the ribbon must be positioned relatively precise with respect to the terminals. The position must be determined in accordance with the given geometrical variations occurring for the terminals. For determining the correct position of the ribbon, the two-dimensional properties of both terminals for a given connection must be assessed and the correct position must be determined on this assessment. This is complicated to implement in an automated process.
Moreover, the use of the bonding elements according to the above document implies that the impedance of the final connection must be estimated before a particular suitable bonding element can be selected and mounted on the terminals. That is, the precision of the final coupling depends on how precise the estimation of the final coupling can be made.
The properties of the final coupling may be difficult to assess, because it involves gaining precise knowledge of the geometry, which applies for a given set of terminals. Furthermore, the connection is difficult, if not impossible, to trim after it has been produced.
Prior art document JP-A-09017918, discloses a hybrid integrated circuit in which a semiconductor chip is mounted on a metal plate inserted in a through hole in a circuit substrate, the metal plate and substrate being mounted on a common radiation board.
According to the above document, the terminals of the hybrid integrated circuit are provided at the top of the substrate and disposed adjacent to the semiconductor chip.
Instead of mounting bonding wires directly on gold plating layers on the terminals of the substrate, which is a standard feature in the art, the above document teaches the use of a special bonding pad. Bonding wires are mounted at one end at this bonding pad and at the other end at the semiconductor chip.
According to the above document, conductive adhesive is used extensively except for on the connection between the radiation board and the circuit substrate.
The hybrid integrated circuit according to the above document ensures that the surface of the bonding pads are clean and free from flux whereby a reliable bonding of the bonding wire can be performed at the terminals of the semiconductor chip and the terminals of the substrate. This leads to an enhanced mechanical stability of the connection.
However, the impedance control obtainable according to the device disclosed in JP-A-09017918 is deemed to be at the same level as standard devices in which known wire bonding techniques are used.
Prior art document JP-A-232469 shows a number of terminals being provided with protruding bonding pads for obtaining minimum distances to terminals at fixed specific locations.
One object of the present invention is to set out a connection for a hybrid integrated circuit for which very small impedance values can be obtained accurately and cost effectively.
This object has been achieved by the subject matter defined in independent claim 1.
Another object is to achieve a manufacturing process, which accomplishes such a connection.
This object has been accomplished by the subject matter defined in claim 10.
It is furthermore an object of the present invention to accomplish a connection and a process for manufacturing such a connection in which the impedance of the connection can be controlled on an individual basis for each set of terminals.
This object has been accomplished especially according to the subject matter set forth in claims 2 and 11, respectively.
Further advantages will appear from the above discussion, and the following claims and description.
Among the further important advantages of the invention is that a connection of high mechanical stability has been provided.